Erythropoietin (epo) is the primary regulator of RBC production. The level of oxygenation of the kidney, the site of epo synthesis, is thought to play a major role in epo production. The applicant intends to examine the relationship between tissue oxygenation and epo production. As modulation of the oxygen equilibrium curve induced by changes in such parameters as 2,3-DPG levels (as found in chronic renal disease), etc., or in the hemoglobin molecule (e.g. as found in sickle cell disease) affects O2 delivery to the kidney, it is important to know whether the epo level correlates with the degree of P50 displacement. Patients with renal disease and with hemoglobinopathies will be studied, as they all have shifts in the Hb O2 equilibrium curves. Epo titers will be correlated with RBC parameters such as P50 and 2,3-DPG levels, as well as hematocrit and hemoglobin concentrations. The radioimmunoassay (RIA) for epo, which can detect normal and less than normal levels of human epo, will be used to measure serum titers. The molecular heterogeneity of the circulating epo in these clinical disorders will also be examined, using gel chromatography and the RIA. The role of renal oxygenation will be further pursued in vitro, using kidney cells in suspension and a line of renal carcinoma cells developed by the applicant. Hormonal and other factors will also be examined. The RIA will be used to measure epo in the supernatant and extracted from the cells. These studies will aid in the clinical management of the anemia of chronic renal disease. Epo produced in this disorder may not be biologically active, perhaps consisting of molecules larger or smaller than native. The shift to the right in the O2 equilibrium curve may eliminate the patient's ability to correct the anemia by increasing endogenous production of epo, indicating that treatment with exogenous epo may be required.